More on mould and microbes
Under warm, moist conditions, mould can grow out of sight on construction materials and on interior finishes. Mould thrives when a spore lands on a surface where organic food (such as fibres, starches, and cellulose) and moisture are present, and temperatures are 5 to 38 C (40 to 100 F). Mould can grow rapidly in as little as 24 hours.
If stains and mould become visible on the room-side surface of ceiling panels, it is an indication that microbial contaminants may be extensive, affecting the air quality and becoming a concern for the occupants’ health, and eventually, buildings’ structural integrity and long-term value.
As part of mould prevention and interior moisture control, one must be aware of managing relative humidity and condensation. For example, some schools may turn off their HVAC systems during the summer months, thereby increasing the potential for the growth of mould and mildew. CCOHS notes, “Relative humidity levels above 70 per cent may lead to the development of condensation on surfaces and within the interior of equipment and building structures. Left alone, these areas may develop mould and fungi.”
Following controlled humidity and temperature protocols outlined in ASTM International’s D3273-21, Standard Test Method for Resistance to Grown of Mold on the Surface of Interior Coatings in an Environmental Chamber, the surface of ceiling panels and other finishes can be tested to evaluate their resistance to microbial growth. In compliance with this qualitative testing standard, a material test sample is suspended in an environmental chamber above the organism species in soil. The three-tested organism species are aureobasidium pullulans, aspergillus brasiliensis, and penicillium citrinum.
The sample material’s surface is examined under a microscope before the test begins and at the 28-day incubation period. The level of fungal defacement on the test sample is rated on a scale of zero to 10, where 10 indicates no visual defacement. For greater confidence in specifying mould-resistant surfaces, check with acoustic ceiling product manufacturers to review whether their products have been tested to ASTM D3273-21.
Specialty and controlled environments, such as clean rooms and medical establishments, require an even greater level of assurance. The internationally recognized Norme Française (NF) S 90-351:2013-04, Établissements de santé – Zones à environnement maîtrisé – Exigences relatives à la maîtrise de la contamination aéroportée, currently is considered the most stringent test standard within the industry concerning the control of airborne contamination. There is no equivalent for NF S 90-351:2013 in Canada or the U.S.
NF S 90-351:2013 requires material test samples meeting this standard are exposed to aspergillus brasiliensis, candida albicans, and methicillin-resistant straphlococcus aureus (MRSA). Stone wool ceiling panels have achieved an M1 classification, fulfilling the requirements of Zone 4, the standard’s highest risk category.
Ceilings composed of organic fibres and water-based materials need to add a biocide, fungicide, or antimicrobial to help protect against the mould and mildew. With the added chemicals, these materials may become a potential pollutant source contributing to poor IAQ. Other disadvantages of using antimicrobials can include increased resistance to antibiotics, a false sense of security, and increased costs.